Machine-to-machine communication that supports automated or self-sustained communication between terminal devices without human intervention is being developed. Machine-to-machine communication is also named Machine Type Communication (MTC) at the Third Generation Partnership Projection (3GPP). In 3GPP specification Release 11, network optimization functions for MTC devices have been discussed. In Release 12, coverage enhancement to resist building penetration losses is being discussed.
Coverage enhancement is needed for various channels such as shared channel (SCH), physical broadcast channel (PBCH), physical random access channel (PRACH), physical downlink control channel (PDCCH), physical downlink shared channel (PDSCH), physical uplink shared channel (PUSCH), or physical uplink control channel (PUCCH).
There are a number of types of MTC devices. Some devices such as gas meters, electricity meters, or temperature or moisture sensors transmit data at regular intervals. Some devices are designed to transmit data when a particular event has occurred. In order to allow arbitrary MTC devices to quickly establish radio links regardless of device types, locations, or the environment, random access coverage enhancement is particularly of importance.
To enhance the coverage, it may be conceived to transmit the same information item repeatedly in the time domain. Techniques called automatic retransmission request (ARQ) and hybrid-ARQ combined with error correction are employed on PUCCH. In ARQ, if no acknowledge (ACK) message is received at a sender side within a predetermined time period after transmission of a data frame, the same data frame is transmitted repeatedly up to a predetermined number of times. See, for example, non-patent document 1 listed below.
It is also proposed to transmit a long preamble format at PRACH. See, for example, non-patent document 2 listed below. A technique for applying hybrid-ARQ to a part of the random access procedure is also known.